Single Pulse Energy Research Articles

Study on the soft magnetic properties, corrosion, and wear resistance of Ni–Co–W coatings deposited via laser-assisted electrochemical technique: Potential applications in advanced electromagnetic devices

Ni–Co–W alloy possesses several advantages, including exceptional hardness, outstanding wear resistance, and remarkable high-temperature resistance. The coating exhibits favorable soft magnetic performance when the Co content is high. This study combines the introduction of Co element and laser irradiation to explore the changing mechanisms in the soft magnetic properties, corrosion resistance, and wear resistance. Coatings are electrochemically deposited on copper substrates employing a pulsed current, and a Ni–Co–W coating is assisted-deposited utilizing a picosecond laser with a single pulse energy of 10μJ. The experimental results reveal that when 12 g/L of CoSO4·7 H2O is added to the electrolyte, the Co elements significantly improve the soft magnetic properties of the Ni–Co–W alloy. Meanwhile, the reduction of WO42− is also promoted and the W content is increased (nearly 2.6 times, 1.95 Wt%), thereby obtaining microhardness, corrosion resistance, and wear resistance superior to Ni–W. Laser irradiation effectively increases the W content (nearly 2.3 times, 4.52 Wt%) while reducing surface defect. The increased W content alters the internal crystal structure and refines the grain. Moreover, laser irradiation significantly improves the soft magnetic properties (a 33.17 % increase in Ms, a 12.97 % increase in Hc, and a 5.66 % increase in Mr). This study achieves soft magnetic coatings with excellent corrosion and wear resistance through a laser electrochemical deposition process. It provides new processing ideas and methods for preparing soft magnetic alloy coatings and has broad application prospects in magnetic thin film storage devices and high-frequency electromagnetic devices.

Time- and angular-distribution of ion current in pulse-laser ablation plume of aluminum

Thrust generation through pulse-laser ablation has been proposed for use in propulsion systems in space. However, to achieve a high thrust performance, the energy efficiency must be improved and it is important to determine the behavior of the ablation plume to identify where energy losses occur. In this study, the ion-current distribution of a plume with aluminum ablation was measured. A neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with a wavelength and pulse width of 1064 nm and 9 ± 2 ns, respectively, was used for the ablation. Experiments were conducted at three different fluences: 10, 15, and 20 J/cm2. The fluence was varied in two ways: changing the beam-spot diameter while maintaining the single-pulse energy and changing the single-pulse energy while maintaining the beam-spot diameter. The ion current was measured at various angles using Faraday probes. The generated impulse and reduction mass were also measured. By combining and analyzing the results, the divergence angle of momentum, mean valence of ablated aluminum, and energy efficiencies of several processes were estimated.

Elucidating the transfer dynamics of high-viscosity silver paste for laser-induced forward transfer of continuous line

Laser-induced forward transfer (LIFT), as an innovative 3D direct-write method, has been increasingly applied for various material printing in many applications. Elucidating the transfer process of paste is crucial to manipulate the printing quality. In this work, the transfer dynamics of high-viscosity silver paste in LIFT of continuous line was systematically investigated based on the cumulative effect from images obtained over hundreds of laser pulses. The influences of process parameters, including the laser energy input (single pulse energy, repetition frequency, and scanning speed) and the thickness of paste film, on the bump height and expansion velocity of bump front were analyzed. With increasing the single pulse energy or repetition frequency, or decreasing the scanning speed or film thickness, the evolution of bump morphology and sputtering varies from just a tiny bump with no sputtering, to a moderate-sized bump with a small amount of sputtering and rebounding, and further to a large bump with intense sputtering and rebounding. A non-dimensional group in terms of Reynolds and Weber numbers was proposed to categorize different evolution regimes and claim the physical mechanism on LIFT of continuous line. When the Reynolds number is greater than 0.01 and the Weber number is greater than 0.1, the inertial effect is sufficient to resist the viscous and capillary effects, inducing the paste to bulge and transfer downwards. A moderate-sized bump with no visibly fragmented sputtering is desirable for the transfer of continuous grid lines. The forming status of grid lines can be predicted according to the behavior of paste transfer, and the predicted grid line state agrees well with the actual state. This can provide process and theoretical references for printing continuous grid lines with LIFT.

Effect of Discharge Energy on Micro-Arc Oxidation Coating of Zirconium Alloy.

The micro-arc oxidation (MAO) technique was used to grow in situ oxidation coating on the surface of R60705 zirconium alloy in Na2SiO3, Na2EDTA, and NaOH electrolytes. The thickness, surface morphology, cross-section morphology, wear resistance, composition, and structure of the micro-arc oxidation coating were analyzed by an eddy current thickness measuring instrument, XPS, XRD, scanning electron microscopy, energy spectrometer, and wear testing machine. The corrosion resistance of the coating was characterized by a polarization curve and electrochemical impedance spectroscopy (EIS). The results show that, with the increase in frequency, the single-pulse discharge energy decreases continuously, and the coating thickness shows a decreasing trend, from the highest value of 152 μm at 400 Hz to the lowest value of 87.5 μm at 1000 Hz. The discharge pore size on the surface of the coating gradually decreases, and the wear resistance and corrosion resistance of the coating first increase and then decrease. The corrosion resistance is the best when the frequency is 400 Hz. At this time, the corrosion potential is -0.215 V, and the corrosion current density is 2.546 × 10-8 A·cm-2. The micro-arc oxidation coating of zirconium alloy is mainly composed of monoclinic zirconia (m-ZrO2) and tetragonal zirconia (t-ZrO2), in which the content of monoclinic zirconia is significantly more than that of tetragonal zirconia.

Research on key factors of pulsed CO2 laser annealing of Ge core fiber

The germanium (Ge) core fiber with a core diameter of 29–32 μm and a cladding diameter of 158–162 μm was annealed by pulsed CO2 laser, exploring the key factors determining the properties of annealed Ge core fiber. The experimental results shown that the single pulse energy and the laser scanning speed are key factors of pulsed CO2 laser annealing of Ge core fibers. The reasons for experimental results were preliminarily analyzed from the perspectives of Ge atomic instantaneous kinetic energy and temperature field of Ge core during annealing. For different frequencies of laser annealing, optimal samples with similar properties can be obtained by adjusting the single pulse energy and laser scanning speed. For the samples annealed by 30 kHz, 50 kHz, 60 kHz, and 70 kHz lasers, the optimal Raman frequency average value is 301.191 cm−1, 301.107 cm−1, 301.153 cm−1, and 301.174 cm−1; the lowest propagation loss is 2.174 dB/cm, 2.596 dB/cm, 2.387 dB/cm, and 2.312 dB/cm respectively, which were measured using a quantum cascade laser with the wavelength range from 4.7 to 4.9 μm.

Multivariate optimization effectiveness model of single-longitudinal-mode laser under pre-laser Q-switching regime.

The optimal effectiveness model for optimizing the system parameters was established in this study by combining the optimization function based on the pre-laser Q-switching technique. By introducing boundary conditions to solve the rate equations, the specific process of composite mode selection is analyzed, and the specific pre-laser modulation time interval that enables single-longitudinal-mode laser output is obtained. Furthermore, through the established efficiency evaluation function for single-longitudinal-mode laser output characteristics, with the maximization of single-pulse energy as the objective, an energy efficiency analysis of relevant parameters in the mode selection components is conducted. The model we have established is universal, which can accurately control the pre-laser Q-switching process and reveals the inherent logical relationship of the relevant parameters in composite mode selection. The output characteristics of a single-longitudinal-mode Q-switching laser can be predicted and adjusted under the condition of high pump injection. Both simulation and experimental results confirm the effectiveness of the model.

Laser-Induced Breakdown Spectroscopy Analysis of Sheet Molding Compound Materials

Sheet Molding Compound (SMC) materials are extensively utilized as high-voltage insulation materials in electrical equipment. SMC materials are prone to aging after long-term operation. Conducting non-destructive testing to assess their electrical and physicochemical properties is crucial for the safe operation of electrical equipment. This study identifies the optimal equipment parameters for testing SMC materials using Laser-Induced Breakdown Spectroscopy (LIBS) technology through experimental investigation and also explores the ablation characteristics of SMC under various laser parameters. The results indicate a significant positive correlation between the ablation depth and laser pulse number, while there is no correlation with single laser pulse energy. However, the ablation area demonstrates a strong positive correlation with both single laser pulse energy and laser pulse number. Additionally, LIBS spectral analysis provides elemental results comparable to Energy Dispersive Spectroscopy (EDS), facilitating the examination of variations in Na, Ti, Fe, Mg, Ca, and C elemental contents with depth. Moreover, an enhanced iterative Boltzmann plot method is suggested for calculating the plasma temperature using 21 Fe I spectral lines and the electron density using the Fe II 422.608 nm line. The variations of these plasma parameters with laser pulse number are documented, and the results show consistent trends, confirming that the laser-induced SMC plasma adheres to local thermodynamic equilibrium.

Multi-pulse femtosecond laser ablation of SiC/SiC composites: Morphological evolution, oxidation mechanisms and component characterization

SiC fiber reinforced SiC matrix (SiosC/SiC) composites processed by femtosecond laser play a pivotal role in thermal protection systems. This paper reveals the ablation characteristics of multi-pulse femtosecond laser ablation of SiC/SiC composites, including morphological evolution, oxidation mechanisms and component characterization by heat accumulation simulation and advanced experimental analysis. The results show that the ablation depth induced by the heat accumulation effect is an exponential function of laser parameters. Morphological analysis and component characterization indicate that two types of ablation regions are formed, normal ablation region is an oxidized zone induced by passive oxidation mechanism, and central ablation region is a non-oxidized zone induced by active oxidation mechanism. The increase of single pulse energy and decrease of scanning speed enhance the driving force of chemical reactions, thus dramatically affecting the gas hole and graphite properties in the normal ablation region. Furthermore, the propagation path of thermal stress-induced cracks is determined which emerges from the center ablation region, extending through gas holes to the normal ablation region.

2.1–2.2 μm wavelength-tunable cascade gain modulation Raman fiber laser

We present a theoretical and experimental analysis of a mid-infrared wavelength-tunable cascade gain modulation Raman fiber laser. Our simulation model incorporates the Generalized Nonlinear Schrödinger Equation with the fiber Bragg grating transmission functions. Utilizing the pulse tracking method, we investigate and analyze the impact of pump pulse width and Raman gain fiber length on the first and second order Raman laser thresholds. Additionally, we exhibit the evolution process of the pulse and optical spectrum at a constant pump pulse energy. Furthermore, we present the output pulse width and energy, and the Raman laser center wavelength as a function of the pump pulse energy. Subsequently, using the optimal theoretical values of pump pulse width and Raman gain fiber length, we experimentally achieve the gain modulation Raman fiber laser. With a 1990 nm laser pumping, the Raman laser can produce a 2172 nm laser with a pulse width of 1.25 µs and a single pulse energy of approximately 400 nJ. When tuning the pump laser wavelength from 1950 nm to 2030 nm, the gain modulation Raman laser wavelength can vary from 2130 nm to 2215 nm. Importantly, our experimental results closely align with the theoretical predictions. This study provides valuable insights for the investigation of gain modulation Raman fiber lasers.

The high energy spaceborne all-solid-state lasers based on fluid-loop cooling system

We demonstrate a 532.2 nm high-power all-solid-state pulse laser with a repetition rate of 85 Hz, a single pulse energy of 215.8 mJ. The lasers spot size is (3.8, 3.6) mm, and the divergence angle is (0.57, 0.69) mrad. The stable working state of this laser last for 402 s and the pointing stability of the output beam is better than 50 μrad. A fluid loop system based on phase-change energy-storage heat exchanger is designed in this paper in order to solve several key problems induced by the heat dissipation. The laser is working normally in orbit, and it lays the foundation for the development of spaceborne all solid-state laser with high-energy, high-repetition rate.

CH3NH3PbBr3 as a saturable absorber for infrared passively Q-switched solid-state laser

Perovskite materials are used in the field of lasers and can achieved good results. In this paper, we prepared an organic–inorganic hybridized CH3NH3PbBr3 saturable absorber (SA). Continuous wave (CW) Tm:YAP solid-state lasers with CH3NH3PbBr3-SA successfully obtained pulsed lasing at 1987.5 nm after continuous tuning. In CW mode, the maximum absorbed pump power by the laser was 19.42 W, which corresponds to 0.68 W output power. The central output wavelength of the continuous wave laser was 1989.9 nm. In PQS mode, the output power of laser was 203 mW. Under the condition of maximum repetition frequency of 45 kHz, the narrowest pulse width of the PQS laser were 1.16 μs. Meanwhile, the laser produced a maximum single-pulse energy (4.5 μJ) and a maximum peak power (3.9 W). The beam quality factors (the horizontal/vertical directions) were M2 x = 1.1 and M2 y = 1.39. The CH3NH3PbBr3 was an excellent SA for infrared PQS solid-state lasers, which had a large potential for development applications in the field of lasers.

Ag/MXene as Saturable Absorber for Tm:Ho Co-Doped Q-Switched Fiber Laser.

Q-switched fiber lasers have become reliable light sources for generating high-energy pulses, which can be passively modulated by saturable absorbers with excellent nonlinear optical properties. The composite combining Ag and MXene exhibits a broadband nonlinear response and high modulation depth, making it a promising candidate for saturable absorbers in pulsed lasers. Herein, we demonstrate a Q-switched Tm:Ho co-doped fiber laser centered at 2 µm, where the Ag/MXene composite serves as a saturable absorber to generate pulses. The typical spectrum, pulse train, and radio frequency spectrum of Q-switched pulses were observed, in which the 60 dB signal-to-noise ratio was higher than that of 2 µm Q-switched fiber lasers based on other materials, demonstrating the stability of the output pulses. Additionally, the long-term stability of the laser was evaluated over 2 h, where the well-maintained central wavelength and output power also indicated the robustness of the Q-switched laser. Furthermore, the influence of the pump power on the parameters of Q-switched pulses was also investigated, which is conducive to control the output characteristics of lasers. Specifically, the pulse width of the Q-switched pulse decreased, while the repetition rate, output power, and single pulse energy all increased with the increase in pump power. These experimental results demonstrate the ability of Ag/MXene as a saturable absorber and show its potential for generating high-performance pulses in ultrafast lasers.

High-energy, high-peak-power diode-pumped Q-switched Tm:YAG laser at 2.02 μm with tunable repetition rate from 100 Hz to 1000 Hz

A high-energy, high-peak-power Q-switched Tm:YAG laser at 2.02 μm with a tunable repetition rate from 100 Hz to 1000 Hz and pulse duration in the hundreds of nanoseconds is demonstrated. The high energy output was achieved by employing a thermally stable linear cavity, including two compact laser diode continuous-wave side-pumped Tm:YAG laser modules. For Q-switched operation, stable Q-switched performance from 100 Hz to 1000 Hz was realized at near-room temperature. At a repetition rate of 100 Hz, the laser delivered a maximum pulse energy of 215 mJ with a pulse duration of 124.4 ns, resulting in a peak power of up to 1.73 MW. When the repetition rate was tuned to 200 Hz, 500 Hz, and 1000 Hz, pulse energies of 212 mJ, 125.6 mJ, and 68.2 mJ were obtained, with pulse durations of 133.6 ns, 176.3 ns, and 262 ns, respectively. To the best of our knowledge, these results represent the highest single pulse energies and peak powers ever accomplished for a diode-pumped Q-switched Tm-doped 2 μm laser operating at high repetition rates exceeding 100 Hz.

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

A High-Energy, Wide-Spectrum, Spatiotemporal Mode-Locked Fiber Laser.

In this article, we demonstrate a high-energy, wide-spectrum, spatiotemporal mode-locked (STML) fiber laser. Unlike traditional single-mode fiber lasers, STML fiber lasers theoretically enable mode-locking with various combinations of transverse modes. The laser can deliver two different STML pulse sequences with different pulse widths, spectra and beam profiles, due to the different compositions of transverse modes in the output pulses. Moreover, we achieve a wide-spectrum pulsed output with a single-pulse energy of up to 116 nJ, by weakening the spectral filtering and utilizing self-cleaning. Strong spatial and spectral filtering are usually thought to be necessary for achieving STML. Our experiment verifies the necessity of spatial filtering for achieving STML, and we show that weakening unnecessary spectral filtering provides an effective way to increase the pulse energy and spectrum width of mode-locked fiber lasers.

High energy and high repetition rate QCW-LD end-pumped electro-optical Q-switched Yb:YAG laser

The quasi-continuous wave laser diode (QCW-LD) pumping is considered as the most efficient way for generating high energy nanosecond pulsed laser with repetition rate ranging from 50 to 1000 Hz. Here, a high efficiency, high repetition rate and high energy QCW-LD end-pumped electro-optical (EO) Q-switched Yb:YAG laser was demonstrated. The shortest pulse duration of 17.4 ns with a maximum single pulse energy of 5.1 mJ was obtained at the repetition rate of 100 Hz. As the repetition rate increases up to 500 Hz, the maximum output single pulse energy was obtained to be 5.38 mJ with the pulse width of 18.7 ns, corresponding to the slope efficiency of 21.6% and beam quality factor of M x 2=1.04, and M y 2=1.01. In addition, a theoretical study was carried by numerical simulation of the rate equations, and the results were agreed well with the experimental ones. The results show that QCW-LD pumping with Yb-doped crystals is a promising way for highly efficient, high-energy and high repetition rate nanosecond pulsed laser generation.

Polarized spectral properties and 2.3 µm laser performance of the Tm:YVO4 crystal

The polarized spectral properties and ∼2.3 µm high-power continuous-wave laser operation of Tm3+-doped yttrium orthovanadate crystal (Tm:YVO4) are reported. For the 3H4 → 3H5 transition, the stimulated-emission cross-section σSE is 1.01 × 10−20 cm2 at 2276 nm corresponding to a large emission bandwidth of 52 nm (for π-polarization). Pumped by a 794 nm laser diode, the 1.5 at.% Tm:YVO4 laser delivered 5.52 W at 2.29 µm with a slope efficiency of 19.9%, a laser threshold of 8.70 W, and a linear laser polarization (π). The Tm laser operated on the cascade scheme (on the 3H4 → 3H5 and 3F4 → 3H6 transitions) which was mainly responsible for the observed high laser slope efficiency. We also report on the first passively Q-switched Tm:YVO4 laser at 2.3 µm by employing porous nano-grained cuprous selenide (PNG-Cu2Se) as a saturable absorber. The shortest pulse duration and the highest single pulse energy amounted to 706 ns and 3.65 µJ, respectively, corresponding to a pulse repetition rate of 62.8 kHz.

High power self-Q-switched Tm:YAP laser

To the best of our knowledge, the output performance of a self-Q-switched Tm:YAP laser has been controlled by adjusting the cavity length for the first time. By using a concise concave-flat cavity, a pulsed laser emitting at 1993 nm is produced without any additional modulation device. Under a stable self-Q-switched mode, the maximum average output power of 9.76 W is achieved from the laser when the incident pump power is 28.78 W, corresponding to a slope efficiency of 36.9% and an optical-to-optical conversion efficacy of 33.9%. Also, the narrowest pulse width of 485 ns at 48.97 kHz is obtained from the laser with a single pulse energy of 199.3 µJ. As far as we know, this laser has the highest average power and narrowest pulse width compared to other self-Q-switched Tm:YAP lasers.

The Microchip Laser and Its Drive Control System for Planetary Mass Spectrometry Measurements

To fulfill the requisites of planetary mass spectrometry applications, this paper introduces the creation of a miniaturized, low-power passive Q-switched microchip laser system. The entire system, inclusive of the laser and all electronic components, weighs 106 g, with power consumption below 3 W. The laser output exhibits a pulse duration of 410 ps, accompanied by a single pulse energy of 16.8 μJ. Augmented by the optical focusing system, the system attains a focal spot size of approximately 15 μm and laser irradiance of up to 22 GW/cm2. The driving control system facilitates versatile regulation of parameters such as output current amplitude, pulse duration, and frequency, thereby modulating the laser output frequency and duty cycle. The microchip laser fully meets the power requirements for exciting plasma from planetary rocks and soil.

Tuning SERS performance through the laser-induced morphology changes of gold nanostructures

Differently shaped periodic gold nanostructures on the surface of a thin metal film are fabricated utilizing the direct laser writing technique. The variations in the energy of single femtosecond pulses lead to the formation of morphologically distinct hollow nanostructures. The arrays that excite hybridized plasmonic modes are characterized by electron microscopy and assessed for surface-enhanced Raman spectroscopy (SERS). Plasmonic properties are investigated through SERS using the adsorbed 4-mercaptobenzoic acid (4-MBA) molecules. The development of sharp tips in the nanostructures is initiated by the higher-energy laser pulses, while the structure formation principle itself is altered by the thickening of the film. The change in the structure shape and gold layer thickness tune the SERS signal and the enhancement factor (EF), leading to an EF of 107. Such a factor enables the future prospects of the arrays to be applied for single-molecule detection.